Cognitive Neuroscience - Attention

Defining Attention

• William James (1890) defined attention as the mind's possession, in a clear and vivid form, of one out of several simultaneously possible objects or trains of thought, characterized by focalization and concentration of consciousness. It involves withdrawal from some things to effectively deal with others, contrasting with a confused, dazed state.

The Purpose of Attention

• Limited Biological Resources:

  • Energy metabolism in the brain supports approximately 0.1 spikes/sec/neuron on average.

  • The brain cannot perform an unlimited number of actions simultaneously.

• Not All Stimuli Are Important:

  • Attention helps to ignore irrelevant neuronal signals.

  • Attention helps to boost the reliability of relevant signals.

• Working memory/awareness.

Selective Attention

• Prioritizing certain pieces of information over others.

• Example: Searching for someone in a crowd.

Overt Attention - Eye Movements

• Most direct way to shift attention.

• Poor resolution in the periphery means awareness is primarily of things near the center of gaze (fovea).

• Many actions require eye movements.

  • Looking for a friend in a crowd exemplifies top-down attention, driven by a goal that prioritizes certain features.

  • Attention can also be directed by bottom-up properties of a stimulus that grab attention.

Feature Integration Theory

• Attention: prioritization of information in space.

• In conjunction search, attention to each location is needed to bind the color + shape features.

• Anne Triesman

  • Preattentive Stage: Featural primitives in a visual scene are extracted simultaneously in a parallel process.

  • Focused Attention Stage: Attention is directed in a serial process to a location; primitives are combined to form a whole.

Covert Attention

• Directing focus without moving the eyes.

• Example: Keep your eyes forward, but shift your attention to the right side of the room.

• Researchers might prefer to study covert attention compared to overt attention because it allows them to isolate the effects of attention without the confound of eye movements.

• Helmholtz (1894) first described the idea of covert attention.

Posner Task

• Studying the effects of covert spatial attention.

• Involves cues and targets to assess reaction times (RT).

• Trials:

  • Valid: Cue indicates the correct location of the upcoming target.

  • Invalid: Cue indicates the incorrect location of the upcoming target.

  • Neutral: Cue provides no directional information.

• Results:

  • Reaction times are influenced by the validity of the cue.

  • Position uncertainty.

Selective Attention: Early vs. Late Selection

• Does selection happen early or late in processing?

• The brain has limited capacity to process information (e.g., energy resource limitations).

• The question is: How much sensory information is available for further processing if it is filtered out by selective attention?

• Initial studies tried to answer this question using an auditory dichotic listening task.

Early Selection/Filtering of Information (Broadbent)

• Inputs → Sensory Buffer → Filtering (based on physical characteristics) → Meaning extracted here on after → Short term memory

• Other channel no longer processed after filtering.

• Broadbent (1958)

• Scalp EEG suggests attention influences brain activity as early as ~100 ms after stimulus onset.

• Some information breaks through (e.g., your name - cocktail party effect).

Late Selection/Filtering of Information (Deutsch)

• Input → Sensory Perceptual Meaning Analysis → Filter → Short Term Memory (awareness) → Response.

• Deutsch & Deutsch (1963)

• Somewhat inefficient (fully process all this information only to filter most of it out).

Attenuation Theory (Triesman)

• Input → Sensory Attenuator → Meaning extracted here on after → Short Term Memory.

• Other channel gets attenuated.

• Triesman (1964)

Interim Summary: Selective Attention

• Ways to use attention to select information: overt vs. covert.

• Attention can be deployed/captured in a top-down or bottom-up fashion.

• Studies of covert attention often use a variant of the Posner task.

• Key question: early vs. late selection of information.

Disorders of Attention

• What do lesion patients tell us about what attention is and how it is different from perception?

• What brain structures are critical for using attention?

Visual Neglect

• After lesions to the right parietal lobe, patients may neglect the left visual field.

• Neglect patients fail to reorient to the neglected side of space, unlike hemianopia patients who DO reorient

• Eye movements show that neglect patients ignore one side of space.

• When searching for a target, neglect patients ignore the left visual field.

• Neglect for internal memory representations.

• Descriptions of visual scenes from memory demonstrate viewpoint-specific deficits in internally-directed attention.

Neglect as Attentional, Not Perceptual, Disorder

• How do we know the issue is ‘attention’ and not ‘perception’?

• How do we know that neglect patients perceive stimuli on the ignored side, but this processing fails to rise to the level of conscious attention?

• Berti & Rizzolatti 1992

  • Neglect patients primed with a stimulus in the left hemifield, followed by a stimulus in the right hemifield.

  • Highly Congruent pairs were fastest, even though the patient did not report ‘seeing’ the left side stimulus.

• Cueing attention can also modulate the effects of neglect, suggesting that it is related to attention and not just perception.

• Neglect patients have an especially hard time ‘disengaging’ from an invalid cue when it was in the normal hemifield.

Evidence for Object-Based Attention

• Is attention strictly spatial?

• Dissociation between spatial and object-based neglect.

• Object-based lesions typically more posterior/inferior than spatial neglect lesions.

• The experiment involves valid trials, invalid trials (same object), and invalid trials (different object).

Cognitive and Neural Mechanisms of Attention

• Neglect patients show attentional, not perceptual, deficits.

• How does selective attention affect the way that the brain processes information?

• Scalp EEG suggests attention influences brain activity as early as ~100 ms after stimulus onset.

• Gandhi, Boynton, & Heeger (1999) PNAS.

  • Spatial attention modulates activity in early visual cortex.

  • Activity is increased in V1 in the hemisphere that represents the attended side of space (i.e., contralateral).

• Hopfinger et al, 00

  • Attentional effects are seen in visual cortex in the hemisphere contralateral to the attended target.

  • Observed in preparation for the target.

• Attention resolves competition in higher visual areas.

  • Covert attention to the V4 neuron’s receptive field = no reduction in neural response.

• The experiment involves valid trials, invalid trials (same object), and invalid trials (different object).

Attention Modulates Activity in Higher (Category-Specific) Visual Areas

• Does attending to specific visual categories modulate activity in category-specific visual brain areas?

• FFA: fusiform face area

• PPA: parahippocampal place area

Attention: Modulates Communication Between Lower and Higher Visual Areas

• If attention ‘binds’ the features, does that mean the brain areas that process the features are more ‘connected’?

• Attention modulates connectivity between low and high-level visual areas.

• 'Attend face' or 'Attend house'

• Attention affects the correlation between regions. Inter-region correlation (r).

• Between-region correlation predicts behavioral performance.

• Connectivity predicts behavior

Where Does ‘Attention’ Come From?

• Networks of frontal and parietal areas are thought to deploy attention to sensory brain regions on the basis of:

  • (1) response to environmental stimuli

  • (2) information about goals

• Attention modulates frontal activity similarly with or without a stimulus present.

• Suggests a more abstract signal about the target (or goal/purpose) of the attention.

• More on goals in CH 11.

• FEF = frontal eye fields.